Most microelectronic devices are fabricated by depositing thin metal and dielectric films onto substrates such as silicon, gallium arsenide, and glass. Thin metals and dielectrics are deposited in a vacuum chamber by numerous techniques known in the art such as sputtering, evaporation, and Chemical Vapor Deposition (CVD). Sputtering is a versatile deposition technique because it can be used to deposit a wide variety of materials at relatively high deposition rates. Sputtering is particularly useful for depositing multiple layers of materials.
Sputtering systems typically bias a target comprising the material to be sputtered at a relatively high voltage, typically about -500 volts, in a vacuum chamber filled with an inert gas such as argon, at pressures ranging from 0.1 mtorr to 100 mtorr. The bias potential induces a breakdown of the gas and the formation of a plasma glow discharge. The ions in the plasma are accelerated by the negative potential into the target thereby producing secondary atomic emission, which sputters material on a substrate placed in the path of the sputtered ions. Magnetic fields are typically used to confine the plasma in order to increase the sputtering rate.
It is sometimes desirable to deposit multiple layers of different material on substrates without removing the substrates from the process chamber. However, most prior art sputtering systems are designed to deposit one material, which may be a single metal or dielectric or a combination of several metals or dielectrics. Thus, if multiple layers of different materials have to be deposited on substrates, the sputtering systems usually need to be reconfigured and the substrates have to be cycled from atmosphere to vacuum. Exposing the substrates to atmospheric pressure between depositions may result in the formation of an undesirable interface layer.
It is desirable to process multiple substrates simultaneously in order to increase process throughput and thus reduce the manufacturing costs of the microelectronic devices. Modern semiconductor processing tools, such as cluster tools, process multiple batches of substrates simultaneously. Cluster tools comprise a plurality of process chambers that are clustered around a central platform. A transport mechanism or robot moves the substrates between the various process chambers.
Typically, each process chamber attached to the cluster tool performs a single task and can be operated independent of the other process chambers. For example, the individual process chambers may clean substrates before processing, etch substrates or a film deposited on substrates, or deposit metal or dielectric films on substrates. Typically, the process chambers are configured to deposit only one metal or dielectric film. Consequently, if the process requires multiple layers of metals or dielectric films, the multiple layers are sequentially deposited in different process chambers. State-of-the-art cluster tools typically have between four and eight process chambers. Therefore, cluster tools have a limited capability to deposit multi-layer film coatings.
Some multi-layer films need to be deposited sequentially in one process chamber. Moving the substrates from one process chamber to another process chamber usually changes the pressure and temperature of the substrates. These pressure and temperature changes may result in the formation of an undesirable interface layer between the films.